linux-kernel - Re: [PATCH] remoteproc: Create a separate workqueue for recovery tasks

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Date:   Fri, 08 Jan 2021 13:03:02 -0800
From:   rishabhb@...eaurora.org
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Alex Elder <elder@...aro.org>, linux-remoteproc@...r.kernel.org,
        linux-kernel@...r.kernel.org, tsoni@...eaurora.org,
        psodagud@...eaurora.org, sidgup@...eaurora.org
Subject: Re: [PATCH] remoteproc: Create a separate workqueue for recovery
 tasks

On 2020-12-21 16:35, Bjorn Andersson wrote:
> On Thu 17 Dec 12:49 CST 2020, Alex Elder wrote:
> 
>> On 12/17/20 12:21 PM, rishabhb@...eaurora.org wrote:
>> > On 2020-12-17 08:12, Alex Elder wrote:
>> > > On 12/15/20 4:55 PM, Bjorn Andersson wrote:
>> > > > On Sat 12 Dec 14:48 CST 2020, Rishabh Bhatnagar wrote:
>> > > >
>> > > > > Create an unbound high priority workqueue for recovery tasks.
>> > >
>> > > I have been looking at a different issue that is caused by
>> > > crash notification.
>> > >
>> > > What happened was that the modem crashed while the AP was
>> > > in system suspend (or possibly even resuming) state.  And
>> > > there is no guarantee that the system will have called a
>> > > driver's ->resume callback when the crash notification is
>> > > delivered.
>> > >
>> > > In my case (in the IPA driver), handling a modem crash
>> > > cannot be done while the driver is suspended; i.e. the
>> > > activities in its ->resume callback must be completed
>> > > before we can recover from the crash.
>> > >
>> > > For this reason I might like to change the way the
>> > > crash notification is handled, but what I'd rather see
>> > > is to have the work queue not run until user space
>> > > is unfrozen, which would guarantee that all drivers
>> > > that have registered for a crash notification will
>> > > be resumed when the notification arrives.
>> > >
>> > > I'm not sure how that interacts with what you are
>> > > looking for here.  I think the workqueue could still
>> > > be unbound, but its work would be delayed longer before
>> > > any notification (and recovery) started.
>> > >
>> > >                     -Alex
>> > >
>> > >
>> > In that case, maybe adding a "WQ_FREEZABLE" flag might help?
>> 
>> Yes, exactly.  But how does that affect whatever you were
>> trying to do with your patch?
>> 
> 
> I don't see any impact on Rishabh's change in particular, syntactically
> it would just be a matter of adding another flag and the impact would 
> be
> separate from his patch.
> 
> In other words, creating a separate work queue to get the long running
> work off the system_wq and making sure that these doesn't run during
> suspend & resume seems very reasonable to me.
> 
> The one piece that I'm still contemplating is the HIPRIO, I would like
> to better understand the actual impact - or perhaps is this a result of
> everyone downstream moving all their work to HIPRIO work queues,
> starving the recovery?
> 
Hi Bjorn,
You are right, this is a result of downstream having HIPRIO workqueues
therefore starving recovery. I don't have actual data to support the 
flag
as of now. If needed for now we can skip this flag and add it later with
sufficient data?
> Regards,
> Bjorn